Stella uses default CentOS kernel, which is heavily server-oriented, right? Is there a repository with new (or at least LT 3.4) kernel that was configured for desktop use? I mean, I'm on hardware where things like preemption, timer frequency etc. actually do make a difference. Newer kernel also helps, I'm already on 3.8 from ElRrepo, but I believe it can be better.

I wasn't able to find anything on Google, but then I'm not a RHEL/CentOS expert .

I understand your situation, but we don't have the man power to maintain kernels. What you can do is get in touch with Toracat of the Elrepo project who also maintains the CentosPlus kernels and see if there's something that can be done.